An electromechanical pressure sensor generally comprises a membrane made of silicon or of a silicon alloy having piezoelectric strain gauges fitted on its front face that are arranged as a Wheatstone bridge and connected to an electronic processor unit by connection wires. The rear face opposite from the face carrying the strain gauges is subjected to a pressure that is to be measured, which pressure, by deforming the membrane, strains the gauges and enables the pressure to be measured electrically. The membrane is generally mounted on a support that is also made of silicon. Since silicon is particularly sensitive to electrochemical attack, the membrane is mounted at one end of a duct filled with a transfer fluid, generally silicone oil. The other end of the duct is closed by a pellet of stainless steel having its outside face in contact with the fluid of pressure that is to be measured. The pressure applied to the stainless steel pellet is transmitted via the transfer fluid to the silicon membrane and is measured by the processor unit on the basis of signals supplied by the strain gauges. The electrical signal generated by the processor unit is then transmitted to a communication network.
The sensor as obtained in this way is generally bulky, heavy, and expensive, in particular because of the presence of the duct filled with oil and of the associated sealing elements. Specifically, the oil must be absolutely incompressible, and such oils are expensive and freeze at low temperature to such an extent as to transmit vibration. If they are not totally free of impurities and/or free radicals, such oils generate electrical drift when they are subjected to an electric voltage. The cylindrical duct must be filled in extremely rigorous manner since the presence of any air in the duct would make the sensor inaccurate, or even inoperative. Performing this operation and inspecting it increase the cost of producing the sensor. The membrane of the sensor is generally fitted on the support of the sensor by adhesive or by brazing. This junction must be leaktight so as to avoid any intrusion of fluid under the membrane, which would end up ruining the sensor. Such operation suffers from the variability that is associated with being performed manually, and it is a recurrent source of defects. Finally, such a sensor is extremely sensitive to rapid variations in the temperature of the fluid of pressure that is to be measured. Specifically, although piezoelectric sensors are well known for presenting low sensitivity to temperature variations, the behaviors of the transfer fluid and of the duct lead to errors that are difficult to compensate. Finally, at extremely low temperatures, the transfer fluid can freeze and make the sensor inoperative.
Resistive sensors require regular calibration in order to conserve an acceptable level of accuracy, in particular because of their sensitivity to temperature. Calibrating a piezoelectric sensor generally requires a calibrated measurement device to be connected to its terminals, so it must be possible to access the sensor physically. Such an operation requires the equipment in which the sensor is mounted to be taken out of operation, which leads to down-time that is harmful, particularly for sensors on board aircraft. Finally, an operating defect of a piezoelectric sensor can be difficult to distinguish from a defect in the transmission circuit. It is then necessary to provide local systems for monitoring operation.